01 - In a large mixing bowl, whisk together the soy sauce, mirin, honey, brown sugar, rice vinegar, minced garlic, grated ginger, and sesame oil until the sugars dissolve and the mixture is well combined.
02 - Add the chicken thighs to the bowl and turn each piece to coat thoroughly. Cover and refrigerate for at least 30 minutes, or up to overnight for deeper flavor penetration.
03 - Preheat the oven to 400°F. Line a baking tray with parchment paper or aluminum foil for easier cleanup.
04 - Remove the chicken thighs from the marinade, reserving all the liquid. Place the thighs skin-side up on the prepared baking tray, spacing them evenly apart.
05 - Roast the chicken for 35 to 40 minutes, basting generously with the reserved marinade after the first 20 minutes. Continue roasting until the internal temperature reaches 165°F and the skin is golden and caramelized.
06 - While the chicken roasts, pour the remaining marinade into a small saucepan and bring to a boil. For a thicker glaze, dissolve the cornstarch in cold water and whisk it into the boiling sauce. Simmer for 3 to 5 minutes, stirring occasionally, until the sauce is glossy and coats the back of a spoon.
07 - Transfer the roasted chicken thighs to a serving platter. Drizzle with the reduced teriyaki sauce and garnish with sliced green onions and toasted sesame seeds. Serve immediately while hot.